Unfortunately, there's no reply, but I have been continuing test run.
Then, as far as I checked, there's no segfault with mpi_leave_pinned=0 or
OMP_NUM_THREADS < 4. On the other hand, when I set mpi_leave_pinned=1
(and OMP_NUM_THREADS>=4), I often get segfault.

Because most of segfaults occur in opal_memory_ptmalloc2 as shown below,
I doubt that the cause of segfault is openmpi's memory management in
multi-thread. I ask you to investigate this problem again.